Gaieus has posted an excellent visual response for the error in SketchUp: http://www.google.com/support/forum/p/sketchup/thread?tid=65a6f337a77e8197&hl=en

You will note that solar positioning for noon should be due South, not 8-10 minutes into the afternoon, and that the apparent declination of the sun is lower than it should be for the day and locale. These are potential errors in the equation of time and translational errors that may be due to assuming the surface of the SketchUp model is at the center of the Earth. By viewing the full forum discussion linked above, you can observe that the SketchUp developers do not appear to know of the original scientific literature that initiated this model. This is a matter of professional documentation that has not been updated with the expanded user base, and this is an ethical problem found when coding poplar software based on science.

A SketchUp employee's responses to my concerns from case #565706984 (Jan 4 and 13, 2010):

@unknownuser said:

"We've done some investigation over the weekend, but we don't actually have any more information to provide. We don't have a particular reference document, paper, or source for our algorithms, so there isn't a location to which we could point you for reference. Furthermore, the solar calculations were implemented early on in SketchUp's development, and the people who initially worked on them are no longer with the company."
AND
@unknownuser said:

"As we mentioned before, the solar calculations in SketchUp were written a long time ago without a specific reference to the academic source."